Hydraulic antivibration device and hydraulic antivibration assembly containing the same

ABSTRACT

There are provided a hydraulic antivibration device and an assembly incorporated thereby capable of obtaining a low dynamic spring characteristic upon input of relatively small amplitude vibrations and reducing sufficiently strange sounds. The low dynamic spring characteristic is obtainable by absorption of hydraulic pressure fluctuations between both liquid chambers  6 A,  6 B due to reciprocating displacement of an elastic partition membrane  10.  A first and a second attachment fittings  1, 2  are constituted respectively as body frame side coupling means and as vibration generator or engine side coupling means, whereby part of a vibration transmitting path from partitioning means  7  to the body frame BF can be formed by a vibration-isolating base  3.  Consequently, even when a vibration is generated by impingement of an elastic partition membrane  10  of the partitioning means  7  on plate members, it is possible to suppress securely transmission of the vibration to the body frame by vibration-insulating effect of the vibration-isolating base  3,  thus reducing greatly generation of strange sounds.

TECHNICAL FIELD

This invention relates to a hydraulic (fluid-sealed) antivibrationdevice and a hydraulic antivibration assembly containing the aforesaidhydraulic antivibration device, and more particularly to such ahydraulic antivibration device and an integrated assembly thereof thatare capable of reducing sufficiently strange (unusual) sounds or noisewhile obtaining a low dynamic spring characteristic upon inputting ofrelatively small amplitude vibrations.

BACKGROUND ART

As an antivibration device for supporting and fixing a vibrationgenerator such as an automotive engine or transmission so as not totransmit its vibration to a vehicle body frame, a hydraulic styleantivibration device is well known.

This hydraulic antivibration device is, in general, made up of a firstattachment fitting designed to be attached to an engine side and asecond attachment fitting to be attached to a vehicle body frame side,wherein both attachment fittings are interconnected by avibration-isolating base composed of a rubber-like elastomer. At thesecond attachment fitting a diaphragm is attached, whereby between thediaphragm and the vibration-isolating base there is formed aliquid-filled chamber.

The liquid-filled chamber is divided by a partitioning means into afirst liquid chamber and a second liquid chamber, both of which are putinto communication with each other through an orifice. According to thishydraulic antivibration device, a fluidization effect of a fluid betweenthe first liquid chamber and the second liquid chamber and a vibrationdeadening effect of the vibration-isolating base perform a vibrationdamping function and a vibration insulating function.

There exists another hydraulic antivibration device, such that thepartitioning means is constructed of an elastic partition membrane and apair of displacement-regulating members regulating the displacementamount of the elastic partition membrane from its both sides.

According to the hydraulic antivibration device of this style, when arelatively small amplitude vibration is input, the elastic partitionmembrane reciprocates to be displaced, thereby absorbing the hydraulicpressure fluctuations between both liquid chambers, whereby a lowdynamic spring characteristic is obtainable. On the other hand, when arelatively large amplitude vibration is input, for example, owing toirregular road surfaces upon travelling, the displacement-regulatingmembers serve to regulate the displacement amount of the elasticpartition membrane from both sides to raise the stiffness of themembrane thereby to facilitate fluidization of fluid between both liquidchambers through the orifice, so that a high damping characteristic canbe obtained.

However, a problem with this style of hydraulic antivibration device wasthat because of the construction that the elastic partition membrane isstruck (made into abutment) on the displacement-regulating members, thedisplacement-regulating members oscillate at the time of striking, whichoscillation is transmitted to the vehicle body frame and results ingeneration of strange sounds.

To address this problem, for example, the thickness of the membrane ismade larger or the hardness of the rubber is made higher, therebyheightening the membrane stiffness of the elastic partition membrane tomake it difficult for the elastic partition membrane to do reciprocatingdisplacement, whereby the striking of the membrane on thedisplacement-regulating members can be precluded to suppress thegeneration of strange sounds. In this case, however, the elasticpartition membrane is difficult to deform, complying with the hydraulicpressure fluctuations between both liquid chambers, so that it becomesdifficult to absorb the hydraulic pressure fluctuations and it is unableto obtain a low dynamic spring characteristic.

In the circumstances, heretofore, the contact area of the elasticpartition membrane with the displacement-regulating members has beenmade small by providing the displacement-regulating members with radialribs, whereby the generation of strange sounds has been suppressed, asdisclosed, for example, in JP Patent Publication 6-221368A (PatentReference 1).

-   -   [Patent Reference 1] JP Patent Application Publication 6-221368A        (FIG. 4, etc.)

DISCLOSURE OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

With the prior art construction as described above, however, there was aproblem in that strange sounds attributed to impingement of the elasticpartition membrane on the displacement-regulating members could notsufficiently be reduced. Further problem with the prior art constructionwas that it was unable to efficiently subject the elastic partitionmembrane to reciprocating displacement and a sufficient low dynamicspring characteristic could not be obtained.

The present invention has been made to solve the problems stated above,and is aimed at providing a hydraulic antivibration device and ahydraulic antivibration assembly containing the aforesaid hydraulicantivibration device capable of obtaining a low dynamic springcharacteristic upon inputting of relatively small amplitude vibrationsand sufficiently reducing strange sounds.

MEANS OF SOLUTION OF THE PROBLEMS

In order to achieve the object, the hydraulic antivibration device asset forth in claim 1 comprises a first attachment fitting, a cylindricalsecond attachment fitting, a vibration-isolating base connecting thesecond attachment fitting and the first attachment fitting and composedof a rubber-like elastomer material, a diaphragm attached to the secondattachment fitting to form a liquid-filled chamber between the diaphragmand the vibration-isolating base, partitioning means comparting theliquid-filled chamber into a first liquid chamber on thevibration-isolating base side and a second liquid chamber on thediaphragm side, and an orifice formed between an outer peripheral faceof the partitioning means and an inner peripheral face of the secondattachment fitting and putting the first liquid chamber and the secondliquid chamber into communication with each other; the partitioningmeans including an elastic partition membrane composed of rubber-likeelastomer material and a pair of displacement-regulating membersregulating the displacement amount of the elastic partition membranefrom both sides and having respective openings, wherein the openingsinclude a first opening formed on a radially central side and aplurality of second openings formed around the first opening in adistributed manner; the elastic partition membrane is made up of athick-walled portion situated within the first opening when viewed in anaxis center direction and on radially central sides of thedisplacement-regulating members, a thin-walled portion located radiallyoutwardly of the thick-walled portion and formed thinner than thethick-walled portion thereby being spaced apart from the pair of thedisplacement-regulating members, a stationary portion located at aperipheral margin of the thin-walled portion and pinched and securedbetween the pair of the displacement-regulating members radiallyoutwards of the second openings, first ribs situated at one face of thethin-walled portion around the thick-walled portion in a distributedmanner and formed integrally with a boundary between the thick-walledportion and the thin-walled portion in a spaced relation to the one ofthe pair of the displacement-regulating members, and second ribssituated at the other face of the thin-walled portion around thethick-walled portion and formed integrally with a boundary between thethick-walled portion and the thin-walled portion in a spaced relation tothe other of the pair of the displacement-regulating members; the firstattachment fitting is constituted as coupling means coupled to a vehiclebody frame side and the second attachment fitting is constituted ascoupling means coupled to a vibration generator side, whereby a part ofa vibration transmitting path from the partitioning means to the vehiclebody frame is constituted by the vibration-isolating base.

The hydraulic antivibration device as set forth in claim 2 is directedto the hydraulic antivibration device as set forth in claim 1, whereinthe first and the second ribs are disposed in a radial fashion relativeto the axis center when viewed in the axis center direction of theelastic partition membrane and equidistantly in the circumferentialdirection.

The hydraulic antivibration device as set forth in claim 3 is directedto the hydraulic antivibration device as set forth in claim 1 or 2,wherein the first and the second ribs are provided, on opposite facesthereof to the pair of the displacement-regulating members, with topportions in a projecting manner, the top portions being set in such aheight dimension that they are situated to be spaced apart from the pairof the displacement-regulating members upon assembling of thepartitioning means.

The hydraulic antivibration device as set forth in claim 4 is directedto the hydraulic antivibration device as set forth in claim 1 or 2,wherein the first and the second ribs are provided, on their oppositefaces to the pair of the displacement-regulating members, with topportions in a projecting manner, the top portions being set in such aheight dimension that they are situated to abut on the pair of thedisplacement-regulating members upon assembling of the partitioningmeans.

The hydraulic antivibration device as set forth in claim 5 is directedto the hydraulic antivibration device as set forth in any one of claims1 to 4, wherein at least on the one face of the thin-walled portion,auxiliary ribs are formed in a residual space thereof other than a spacewhere the first ribs or the second ribs are formed, and the auxiliaryribs are constructed so that their rib height is smaller than and theirrib width is narrower than the first ribs and the second ribs.

A hydraulic antivibration assembly device as set forth in claim 6comprises the hydraulic antivibration device as recited in any one ofclaims 1 to 5 and a vibration generator side bracket coupling theaforesaid hydraulic antivibration device to the vibration generatorside, wherein the second attachment fitting includes a small-diametercylinder portion, a large-diameter cylinder portion having a largerdiameter than the small-diameter cylinder portion, and a step portionjoining the large-diameter cylinder portion and the small-diametercylinder portion; the large-diameter cylinder portion is internallypress-fitted in an inner periphery of the vibration generator sidebracket, and the inner periphery of the vibration generator side bracketis formed with an abutment portion capable of abutting on the stepportion of the second attachment fitting internally press-fitted thereinand jutting radially inwardly.

The hydraulic antivibration assembly as set forth in claim 7 is directedto the hydraulic antivibration apparatus as recited in claim 6, whereinthe second attachment fitting is constructed so that the large-diametercylinder portion thereof is situated on the first attachment fittingside than the small-diameter attachment fitting, and the large-diametercylinder portion is internally press-fitted in the inner periphery ofthe vibration generator side bracket and that in the internalpress-fitting state, the step portion of the second attachment fittingis situated on the first attachment fitting side than the abutmentportion of the vibration generator side bracket.

EFFECTS OF THE INVENTION

According to the hydraulic antivibration device as set forth in claim 1,because the elastic partition membrane is constructed of thethick-walled portion and the thin-walled portion, and the thick-walledportion and the thin-walled portion are respectively formed on aradially center side and radially outwardly, it is possible to make theelastic partition membrane susceptible to reciprocating displacement andto deform it easily, submitting to hydraulic pressure fluctuationsbetween the first and the second liquid chambers. As a result, when arelatively small amplitude vibration is input, the invention effectaccrues that a hydraulic pressure difference between the first and thesecond liquid chambers can be efficiently absorbed and hence a lowdynamic spring characteristic can be ensured.

Further because the thick-walled portion of the elastic partitionmembrane is constructed to be situated within the first opening whenviewed in the axis center direction, it is possible to transmitefficiently hydraulic pressure fluctuations between the first and thesecond liquid chambers through the first opening to the thick-walledportion of the elastic partition membrane. As a consequence, the effectaccrues that the submissive deformation of the elastic partitionmembrane complying with the hydraulic pressure fluctuations can be moreefficiently conducted, thereby ensuring more a low dynamic springcharacteristic.

On the other hand, when a relatively large amplitude vibration is input,the first ribs or the second ribs abut on the displacement-regulatingmembers to regulate the reciprocating displacement, whereby it ispossible to enhance the stiffness of the membrane. As a result, thereaccrues the effect that it is possible to make the fluid susceptible tofluidizing between both liquid chambers, so that a damping function dueto fluidization effect of the fluid is efficiently exhibited and a highdamping characteristic can be obtained.

Moreover because the first ribs and the second ribs are formed at theboundary between the thick-walled portion and the thin-walled portion,the effect accrues that by abutment of the first and the second ribsagainst the displacement-regulating members, it is possible to takeadvantage of effectively the stiffness of the thick-walled portionthereby to enhance more the stiffness of the elastic partition membraneas a whole, as a result of which it is possible to securely obtain ahigh damping characteristic as described above.

And besides, even in this situation (where a relatively largedisplacement is input), because the first ribs and the second ribs arearranged in a distributed manner in the surroundings of the thick-walledportion, it is possible to make the contact area of the elasticpartition membrane with the displacement-regulating members small, sothat there accrues the effect that it is possible to suppress thegeneration of strange sounds attributed to collision of the elasticpartition membrane with the displacement-regulating members by thatdecrement.

Furthermore because the first attachment fitting is constructed as bodyframe side coupling means adapted to be coupled to the vehicle bodyframe side and the second attachment fitting is constructed as vibrationgenerator side coupling means adapted to be coupled to the vibrationgenerator side, it is possible to constitute a part of a vibrationtransmitting path from the partitioning means (the elastic partitionmembrane and the displacement-regulating members) to the vehicle bodyframe by the vibration-isolating base.

As a consequence, even if the elastic partition membrane impinges on thedisplacement-regulating members and the displacement-regulating membersoscillate, the effect accrues that it is possible to suppress reliablythe transmission of the oscillation to the vehicle body frame by reasonof the vibration insulating effect of the vibration-isolating baseconstituting part of the vibration transmitting path and to greatlyreduce the generation of strange sounds.

According to the hydraulic antivibration device as set forth in claim 2,because of the disposition that the first and the second ribs aredisposed in a radial fashion relative to the axis center as viewed inthe axis center direction and equidistantly in the circumferentialdirection, in addition to the effects achieved by the hydraulicantivibration device as set forth in claim 1, there is achieved theeffect that the thick-walled portion can be supported with a uniformforce from its surroundings. As a result, it is possible to prevent aforce from acting unevenly on the thick-walled portion thereby elevatingthe durability and exhibiting more effectively the above-mentionedelevation effect of the membrane stiffness.

According to the hydraulic antivibration device as set forth in claim 3,because of the construction that the top portions are formed onrespective faces of the first and the second ribs opposite to thedisplacement-regulating members and set in a height dimension such thatthe top portions are situated at a spaced relation to thedisplacement-regulating members, an additional effect to the effectsachieved by the hydraulic antivibration device as set forth in claim 1or 2 is attained in that it is possible to make the elastic partitionmembrane more susceptible to reciprocating displacement thereby todeform more easily the elastic partition membrane, complying with thehydraulic pressure fluctuations between the first and the second liquidchambers. As a result, when a relatively small amplitude vibration isinput, it is possible to efficiently absorb the hydraulic pressuredifference between the two liquid chambers to ensure a low dynamicspring characteristic.

Further in the case where for the purpose of obtaining a low dynamicspring characteristic, the height dimension of the top portions is setin such a dimension that they are spaced apart from thedisplacement-regulating members and yet the first and the second ribsimpinge on the displacement-regulating members, the top portions serveas a cushion, so that it is possible to make the first and the secondribs to impinge mildly or moderately on the displacement-regulatingmembers. As a result, there is achieved the effect that it is possibleto obtain a low dynamic spring characteristic and to achieve a greatreduction of strange sounds.

In accordance with the hydraulic antivibration device as set forth inclaim 4, in addition to the effects achieved by the one as set forth inclaim 1 or 2, a further effect is achieved in that because the topportions are formed on the faces of the first and the second ribsopposite to the displacement-regulating members and set in a heightdimension such that the top portions may abut on thedisplacement-regulating members, in the case where the first and thesecond ribs impinge on the displacement-regulating members, attendedwith inputting of a relatively large amplitude vibration, the topportions resist in such a manner that the first and the second ribsimpinge moderately on the displacement-regulating members, andultimately, the generation of strange sounds can be reliably reduced.

Further because it is only the top portions that abut on thedisplacement-regulating members, it is possible to suppress to theminimum that the reciprocating displacement of the elastic partitionmembrane is obstructed, thereby making the elastic partition membrane tosufficiently deform, submitting to hydraulic pressure fluctuationsbetween the first and the second liquid chambers. As a consequence,another effect is achieved in that when a relatively small amplitudevibration is input, it is possible to absorb efficiently a hydraulicpressure difference between the first and the second liquid chambers toobtain securely a low dynamic spring characteristic.

According to the hydraulic antivibration device as set forth in claim 5,additional effect to the effects achieved by the hydraulic antivibrationdevice as recited in any one of claims 1 to 4 is achieved in thatbecause auxiliary ribs are formed at least on the one face of thethin-walled portion and in a residual space thereof other than a spacewhere the first ribs or the second ribs are formed, it is possible tofortify the thin-walled portion, which is inferior in strength among theelastic partition membrane. Therefore it is possible to suppress afailure or the like of the thin-walled portion involved by thedisplacement upon inputting of vibrations thereby enhancing thedurability thereof.

Further because the auxiliary ribs are constructed so that they arelower in rib height and narrower in rib width than the first ribs andthe second ribs, there accrues the effect that it is possible tosuppress a rise in stiffness of the overall elastic partition membraneand to maintain a low dynamic spring characteristic when a relativelysmall amplitude vibration is input.

Where the thin-walled portion impinges on the displacement-regulatingmembers, attended with inputting of relatively large amplitudevibrations, the auxiliary ribs serve as a cushion, so that it ispossible to collide the thin-walled portion moderately with thedisplacement-regulating members and consequently, the effect accruesthat generation of strange sounds can be more securely reduced.

In accordance with the hydraulic antivibration assembly as set forth inclaim 6, in addition to the effects achieved by the hydraulicantivibration device as recited in any one of claims 1 to 5, an effectis attained in that because the second attachment fitting is providedwith the step portion and the vibration generator side bracket isprovided at its inner periphery with the abutment portion, it ispossible to make the step portion to abut on the abutment portion wheninternally press-fitting the second attachment fitting into the innerperiphery of the vibration generator side bracket, thereby performingthe positioning of the press-fitting direction. As a further effect,where the loading in the press-fitting direction acts on the secondattachment fitting, attended by inputting of a large amplitudevibration, the step portion serves to abut on the abutment portion,whereby it is possible to avoid detachment of the second attachmentfitting from the inner periphery of the vibration generator sidebracket.

According to the hydraulic antivibration assembly as set forth in claim7, an additional effect to the effects achieved by the hydraulicantivibration assembly as recited in claim 6 is achieved in that becausethe second attachment is constructed so that the large-diameter cylinderportion may be situated on the first attachment fitting side more thanthe small-diameter attachment cylinder portion and concurrently so thatwhen the large-diameter cylinder portion is internally press-fitted inthe inner periphery of the vibration generator side bracket, the stepportion of the second attachment fitting may be situated on the firstattachment fitting side more than the abutment portion of the vibrationgenerator side bracket, it is possible to preclude more securely thesecond attachment fitting from coming off from the inner periphery ofthe vibration generator side bracket.

Specifically stated, according to the foregoing construction, where thevibration generator side bracket, after the vibration generator issupported and fixed, is displaced in the carrying weight direction(namely, where the second attachment fitting is displaced toward thefirst attachment fitting), elastic recovery force of the compressiondeformed vibration-isolating base works as a force obstructing themovement of the second attachment fitting, so that the second attachmentfitting is liable to be detached from the inner periphery of thevibration generator side bracket. However, according to the hydraulicantivibration assembly as recited in claim 7, the step portion of thesecond attachment fitting abuts on the abutment portion of the vibrationgenerator side bracket, whereby the aforementioned detachment can beavoided.

Incidentally in the case where the vibration generator side bracket isdisplaced in the opposite direction to the carrying load (namely, wherethe second attachment fitting is displaced in the direction recedingfrom the first attachment fitting), the elastic recovery force of thecompression-deformed vibration-isolating base works as a force assistingthe movement of the second attachment fitting, so that the secondattachment fitting is difficult to come off from the inner periphery ofthe vibration generator side bracket, which fact dispenses with anypreventive expedient of the aforesaid detachment.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] is a diagrammatic view showing an operating state of ahydraulic antivibration device in one embodiment of this invention,wherein (a) is a top plan view and (b) is a side elevation when viewedin the arrow direction Ib in FIG. 1(a).

[FIG. 2] is a sectional view of the hydraulic antivibration device takenalong II-II line in FIG. 1(a).

[FIG. 3] (a) is a top plan view of an orifice member and (b) is across-sectional view of the orifice member taken along IIIb-IIIb in FIG.3(a).

[FIG. 4] (a) is a top plan view of a plate member and (b) is a sectionalview of the plate member taken along IVb-IVb line in FIG. 4(a).

[FIG. 5] (a) is a top plan view of an elastic partition membrane and (b)is a sectional view of the elastic partition membrane taken along Vb-Vbline in FIG. 5(a).

[FIG. 6] is a partially enlarged sectional view of the elastic partitionmembrane.

[FIG. 7] (a) is a top plan view of a partitioning means and (b) is asectional view of the partitioning means taken along VIIb-VIIb line inFIG. 7(a).

[FIG. 8] is a representation showing a variation example of the elasticpartition membrane, wherein (a) is a top plan view and (b) is apartially enlarged sectional view of the elastic partition membrane.

[FIG. 9] is a sectional view of the hydraulic antivibration device in amodified example.

DESCRIPTION OF REFERENCE CHARACTERS

-   100 hydraulic antivibration device (part of a hydraulic    antivibration assembly)-   1 first attachment fitting-   2 second attachment fitting-   2 a large-diameter cylinder portion-   2 b small-diameter cylinder portion-   3 vibration-isolating base-   5 diaphragm-   6 liquid-filled chamber-   6A first liquid chamber-   6B second liquid chamber-   20 orifice-   7 partitioning means-   8 orifice member (part of the partitioning means)-   84 plate member (part of a displacement-regulating member)-   84 a first opening-   84 b second opening-   9 plate member (part of a displacement-regulating member, part of    the partitioning means)-   94 a first opening-   94 b second opening-   10, 210 elastic partition membrane (part of the partitioning means)-   11, 211 thick-walled portion-   12, 212 thin-walled portion-   13 stationary portion-   14, 214 first rib-   14 a, 214 a top portion-   15, 215 second rib-   15 a, 215 a top portion-   216 auxiliary rib-   EG engine (vibration generator)-   BF vehicle body frame-   B2, B12 engine side bracket (vibration generator side bracket, part    of the hydraulic antivibration assembly)-   B12 b abutment portion

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of this invention will be hereinafter describedwith reference to the accompanying drawings. FIG. 1 is a diagrammaticview showing the state of use of the hydraulic antivibration device 100in one embodiment of this invention, wherein (a) is a top plan view and(b) is a side elevation when viewed from the arrow direction Ib in FIG.1(a).

The hydraulic antivibration device 100 is a vibration-proof device forsupporting and fixing the automotive engine EG so as not to transmitvibrations of the engine EG to the vehicle body frame BF. As shown inFIG. 1, it is coupled to the body frame BF through the body frame sidebracket B1 and to the engine EG through the engine side bracket B2.

The body frame side bracket B1 is fastened and secured to the body frameBF with a bolt (not shown) inserted through an attachment hole B1 awhereas the engine side bracket B2 is fastened and secured to an engineside member EG1 through a bolt (not shown) inserted through anattachment hole B2 a. As a consequence, a carrying weight directed inthe downward direction in FIG. 1(b) acts on the hydraulic antivibrationdevice 100 supporting and fixing the engine EG

FIG. 2 is a sectional view of the hydraulic antivibration device 100taken along II-II line in FIG. 1(a). In FIG. 2, the first attachmentfitting 1 is indicated, but omitted when viewed in cross-section.

The hydraulic antivibration device 100 is, as shown in FIG. 2, mainlyprovided with the first attachment fitting 1 to be attached to the bodyframe BF side (cf. FIG. 1(b)) through the intermediary of the body frameside bracket B1, the cylindrical second attachment fitting 2 to beattached to the engine EG side (cf. FIG. 1(b)) through the engine sidebracket B2, and the vibration-isolating base 3 interconnecting these andcomposed of a rubber-like elastomer

As illustrated in FIG. 2, the first attachment fitting 1 is fabricatedfrom aluminum alloy in the shape of a generally frustum of cone incross-section that is symmetric about an axis center and upwardly tapersoff, and provided, at its lower end face, with a female screw portion 11for fastening to the body frame BF so as to be recessed upwardly. At thelateral side of the female screw portion 11, a positioning pin 12 forfitting in a recessed portion of the body frame side bracket B1 isprovided so as to project.

The second attachment fitting 2 is, as illustrated in FIG. 2, configuredin a cylindrical form which is open at its upper and lower ends (theupper and lower sides in FIG. 2) from an iron and steel material. Thesecond attachment fitting 2 is constructed to have a step, below which(the lower side in FIG. 2) the large-diameter cylinder portion 2 a isformed and above which (the upper side in FIG. 2) the small-diametercylinder portion 2 b is formed. As shown in FIG. 2, the secondattachment fitting 2 is, at its large-diameter cylinder portion 2 a,internally press-fitted in the inner periphery of the engine sidebracket B2.

The vibration-isolating base 3 is, as depicted in FIG. 2, configuredfrom a rubber-like elastomer in a generally truncated conical shape incross-section that is symmetric about the axis center and downwardlytapers off, and vulcanization bonded between an upper end face and thelateral face of the first attachment fitting 1 and the inner peripheryof the second attachment fitting 2 on its lower end side (mainly thelarge-diameter cylinder portion 2 a).

Thus according to the hydraulic antivibration device 100 in thisembodiment, because the first attachment fitting 1 is constructed as abody frame side coupling means to be coupled to the body frame BF sidewhile the second attachment fitting 2 is constructed as a vibrationgenerators side coupling means to be coupled to the engine EG (vibrationgenerator) side, part of the vibration transmitting path from thepartitioning means 7, which will be later described, to the body frameBF is constituted by the vibration-isolating base 3.

As a result of that, as described later, even if in the partitioningmeans 7, the elastic partition membrane 10 impinges on the plate members84, 94 and the plate members 84, 94 in turn oscillate, the transmissionof the oscillation is securely suppressed by reason of the vibrationinsulating effect of the vibration-isolating base 3 constituting a partof the vibration transmitting path, whereby the generation of strangesounds can be greatly reduced.

At the upper end (the upper side in FIG. 2) of the vibration-isolatingbase 3, as shown in FIG. 2, a rubber membrane 31 covering the innerperipheral face of the second attachment fitting 2 (mainly thesmall-diameter cylinder portion 2 b) is linked thereto. This rubbermembrane 31 is fayed with an orifice-forming wall 81 (cf. FIG. 3) of theorifice member 8, the outer periphery of the plate member 9, and anattachment fitting 51 of the diaphragm 5, which will be later described.

The diaphragm 5 is configured in the form of a rubber membrane having apartial sphere, as illustrated in FIG. 2, from a rubber-like elastomerand attached to the upper end (the upper side in FIG. 2) of the secondattachment fitting 2 (the small-diameter cylinder portion 2 b). As aresult, between the downside of the diaphragm 5 and the upside of thevibration-isolating base 3 there is formed the liquid-filled chamber 6.

In the liquid-filled chamber 6, a non-freezing liquid such as ethyleneglycol (not shown) is sealed. The liquid-filled chamber 6 is partitionedby the partitioning means 7 (the orifice member 8, the plate member 9,and the elastic partition membrane 10), which is later described, intotwo chambers of the first liquid chamber 6A on the vibration-isolatingbase 3 side (the lower side in FIG. 2) and the second liquid chamber 6Bon the diaphragm 5 side (the upper side in FIG. 2).

The diaphragm 5 is vulcanization bonded to the attachment fitting 51 inthe form of a donut shape when viewed from the top plane, and attachedthrough the attachment fitting 51 to the upper end (the upper side inFIG. 2) of the second attachment fitting 2, as shown in FIG. 2.

As mentioned above, the partitioning means 7 comparts the liquid-filledchamber 6 into the first liquid chamber 6A and the second liquid chamber6B, and is made up of the orifice member 8 configured in a generallycolumnar shape from a metal material, the plate member 9 configured in agenerally disc shape from a metal material, and the elastic partitionmembrane 10 configured in a generally disc shape from a metal material.

At the outer periphery of the orifice member 8, an orifice 20 is formedbetween the orifice member and the inner periphery (the rubber membrane31) of the second attachment fitting 2. The orifice 20 is an orificepassage through which to put the first liquid chamber 6A and the secondliquid chamber 6B into communication with each other.

The orifice 20 is put into communication through a cutout 83 (cf. FIG.3) formed in the orifice-forming wall 81 of the orifice member 8 withthe second liquid chamber 6B and through a cutout 93 (cf. FIG. 4) formedin the outer periphery of the plate member 9 with the second liquidchamber 6B.

Here, the assembling of the hydraulic antivibration device 100 isconducted by first fitting the partitioning means 7 and the diaphragm 5in this order from the opening at the upper end of the second attachmentfitting 2 (the upper side in FIG. 2) and subsequently subjecting theentirety of the small-diameter cylinder portion 2 b of the secondattachment fitting 2 to necking working (drawing working) in the radialdirection (the lateral direction in FIG. 2).

As a result of this process, the partitioning means 7 (the plate member9) is, as shown in FIG. 2, pinched and secured between a partitioningmeans-receiving portion 32 provided at the vibration-isolating base 3and the diaphragm 5 in the axis center direction (the vertical directionin FIG. 2) of the hydraulic antivibration device 100. The partitioningmeans-receiving portion 32 is formed as a step portion in a plurality ofplaces (or in the whole circumference) at the upside of thevibration-isolating base 3 and serves to bear the lower end face (thelower side in FIG. 2) of the partitioning means 7 (the plate member 9)by the step portion.

In this assembled state, the partitioning means-receiving portion 32 isdeformed under compression, and the elastic recovery force of it acts onthe lower end face of the partitioning means 7 as a holding power of thepartitioning means 7. Thereby even in the case where a large amplitudeor high frequency vibration is input, it is possible to pinch and securethe partitioning means 7 strongly and stably, thereby precluding anyinfluence on dynamic characteristics attributed to the positionaldeviation of the respective members 8, 9, 10 and resonance.

Now referring to FIGS. 3 to 7, respective members 8, 9, 10 constitutingthe partitioning means 7 will be described in turn. In the descriptionof the respective members 8, 9, 10, FIG. 7, which is a top plan view anda cross-sectional view of the partitioning means 7, is referred toappropriately.

Firstly, the orifice member 8 constituting the partitioning means 7 willbe described with reference to FIG. 3. FIG. 3(a) is a top plan view ofthe orifice member 8 and FIG. 3(b) is a sectional view of the orificemember 8 taken along IIIb-IIIb line in FIG. 3(a).

The orifice member 8 is fashioned in a generally cylindrical shapehaving an axis center and a hollow at its inner periphery, asillustrated in FIG. 3, from a metal material such as aluminum. At theaxially upper end (the upper side in FIG. 3(b)) of the orifice member 8,the orifice-forming wall 81 in a roughly flange form is provided over afull circumference thereof in a projecting manner.

At the outer periphery of the orifice member 8, there is provided alongitudinal wall 82 dividing the orifice 20 (cf. FIG. 2) in thecircumferential direction in a projecting manner. Further theorifice-forming wall 81 is formed at its outer peripheral margin withthe cutout 83, as shown in FIG. 3(a), assuming a roughly U-shape asviewed from the top plane. As stated above, the orifice 20 communicatesthrough the cutout 83 with the second liquid chamber 6B (cf. FIG. 2).

At the inner periphery of the orifice member 8, there is formedintegrally the plate member 84 having a constant thickness as shown inFIG. 3, which is in turn pierced with a plurality of (five in thisembodiment) openings (the first and the second openings 84 a, 84 b) in adistributed manner and formed with displacement-regulating portions 84 cto 84 e alongside of peripheral margins of the first and the secondopenings 84 a, 84 b.

The first opening 84 a is, as shown in FIG. 3, pierced in a circularform in a radially center of the plate member 84, and the secondopenings 84 b are pierced around the first opening 84 a in plural number(four in this embodiment) and disposed in a distributed manner. Therespective second openings 84 b assume such a shape that acircumferentially extending annular hole is divided in a radial fashion,and are disposed in a point symmetry about the axis center of the firstopening 84 a.

As shown in FIG. 3(a), the displacement-regulating portions 84 c and 84e are formed in an annular shape concentric with the first opening 84 awhereas the displacement-regulating portion 84 d is formed in a radialand rectilinear fashion relative to the axis center of the first opening84 a. The width dimensions of the displacement-regulating portion 84 cand the displacement-regulating portion 84 d are nearly of the samewidth and made narrower than the opening width (lateral width in FIG.3(b)) of the second openings 84 b. As a result, the contact area of theorifice member with the elastic partition membrane 10 is made smallerand the hydraulic pressure fluctuations from the second liquid chamber6B can be efficiently transmitted to the elastic partition membrane 10(cf. FIG. 2).

Secondly, the plate member 9 constituting the partitioning means 7 willbe described referring to FIG. 4. FIG. 4(a) is a top plan view of theplate member 9 and FIG. 4(b) is a sectional view of the plate membertaken along IVb-IVb line in FIG. 4(a).

As shown in FIG. 4, the plate member 9 is fashioned in a generallycircular shape having an axis center and a constant thickness from ametal material such as aluminum alloy and defined at its outerperipheral margin with the cutout 93 assuming a roughly U-shape asviewed from the top plane. As mentioned above, the orifice 20communicates through the cutout 93 with the first liquid chamber 6A (cf.FIG. 2).

The plate member 9 is, similarly to the plate member 84 of the orificemember 8, pierced with a plurality of (five in this embodiment) openings(the first and the second openings 94 a, 94 b), and thedisplacement-regulating portions 94 c to 94 e are formed alongside ofthe peripheral margins of the first and the second openings 94 a, 94 b.

The first and second openings 94 a, 94 b and the displacement-regulatingportions 94 c to 94 e are constructed in the same pattern (position,size, shape, etc.) as in the first and second openings 84 a, 84 b andthe displacement-regulating portions 84 c to 84 e formed at the orificemember 8, and the description of them is omitted, accordingly.

Then the elastic partition membrane 10 constituting the partitioningmeans 7 will be described with reference to FIGS. 5 and 6. FIG. 5(a) isa top plan view of the elastic partition membrane 10, while FIG. 5(b) isa sectional view of the elastic partition membrane 10 taken along Vb-Vbline in FIG. 5(a). FIG. 6 is a partially enlarged sectional view of theelastic partition membrane 10.

The elastic partition membrane 10 is accommodated between opposing facesof the plate members 84, 94 (cf. FIG. 7) and has a function ofmollifying the hydraulic pressure difference between the first andsecond liquid chambers 6A, 6B. The elastic partition membrane 10 isconfigured in a generally disc shape from a rubber-like elastomer and,as shown in FIG. 5, mainly made up of the thick-walled portion 11, thethin-walled portion 12, the stationary portion 13 and the first and thesecond ribs 14,15.

The thick-walled portion 11 is situated in a radially nearly center ofthe elastic partition membrane 10 and configured in a generally circularshape when viewed from the top plane, as shown in FIG. 5. The diameterdimension of the thick-walled portion 11 is set so that the thick-walledportion may be situated within the aforesaid first openings 84 a, 94 a(cf. FIGS. 3 and 4) when viewed in the axis center direction in theassembled state of the partitioning means 7 (stated another way, theyare not doubled when viewed in the axis center direction) (cf. FIG. 7).

The thin-walled portion 12 is, as shown in FIGS. 5 and 6, locatedradially outwards of the thick-walled portion 11, and formed to bethinner (for example, ¼ to ½ the thickness of the thick-walled portion11) than the thick-walled portion 11. The thin-walled portion 12 islinked to a middle area in the thickness direction of the thick-walledportion 11, and located in a spaced relation to the plate members 84, 94(cf. FIG. 7).

The stationary portion 13 is, as shown in FIGS. 5 and 6, verticallyprovided on the one face side and the other face side of the thin-walledportion 12 at its peripheral margin, and pinched and secured radiallyoutwards of the second openings 84 b, 94 b (cf. FIGS. 3 and 4) betweenthe plate members 84, 94 (the displacement-regulating portions 84 e, 94e)(cf. FIG. 7).

At each of the top portions of the stationary portion 13, a raisedportion 13 a assuming a roughly arc shape in cross-section is providedas shown in FIG. 6 and serves as a sealing part in the assembled stateof the partitioning means 7, whereby leakage of fluid between the firstand the second liquid chambers 6A, 6B is prevented.

As shown in FIG. 6, the thickness dimension of the elastic partitionmembrane 10 between both raised portions 13 a (the vertical dimension inFIG. 6) is made to be thicker than the thickness dimension at thethick-walled portion 11 and the thickness dimension between the topportions 14 a, 15 a, which is later described.

As shown in FIGS. 5 and 6, the first and the second ribs 14,15 in pluralnumber (eight per one face in this embodiment) are located around thethick-walled portion 11 respectively at the one face side and the otherface side of the thin-walled portion 12 in a distributed state, andformed integrally with a boundary between the thick-walled portion 11and the thin-walled portion 12.

As described above, the elastic partition membrane 10 is composed of thethick-walled portion 11 and the thin-walled portion 12, which arelocated respectively in the radially center and radially outsidethereof, and consequently, it is possible to make the elastic partitionmembrane 10 susceptible to reciprocating displacement thereby deformingit by readily following the hydraulic pressure fluctuatons between thefirst and the second liquid chambers 6A, 6B.

Further because the thick-walled portion 11 of the elastic partitionmembrane 10 is constructed so as to be situated within the firstopenings 84 a, 94 a when viewed in the axis center direction (cf. FIG.7), it is possible to transmit efficiently the hydraulic pressurefluctuations between the first and the second liquid chambers 6A, 6Bthrough the first openings 84 a, 94 a to the thick-walled portion 11 ofthe elastic partition membrane 10.

As a result, since it is possible to perform more efficiently suchsubmissive deformation of the elastic partition membrane 10 to theaforesaid hydraulic pressure fluctuations, when a relatively smallamplitude vibration is input, the hydraulic pressure difference betweenthe first and second liquid chambers 6A, 6B can be efficiently absorbed,thereby obtaining securely a low dynamic spring characteristic.

On the other hand, when a relatively large amplitude vibration is input,the first or the second ribs 14, 15 abut on the plate members 84, 94(displacement-regulating portions 84 c, 94 c) thereby regulating thereciprocating displacement of the elastic partition membrane 10 toenhance the stiffness of the membrane. As a result, it is possible tomake the fluid susceptible to fluidizing between the both liquidchambers 6A, 6B, so that a damping function due to fluidization effectof the fluid can be efficiently exhibited and a high dampingcharacteristic can be obtained.

Moreover because the first and the second ribs 14, 15 are formed at theboundary of the thick-walled portion 11 and the thin-walled portion 12,it is possible to take advantage of efficiently the stiffness of thethick-walled portion 11 by the abutment of the first and second ribs 14,15 against the plate members 84, 94 (the displacement-regulatingportions 84 c, 94 c), thus more enhancing the stiffness of the elasticpartition membrane 10 as a whole. As a result, a high dampingcharacteristic can be ensured as described above.

Here (upon inputting of a relatively large displacement), since thefirst and the second ribs 14, 15 are arranged in the surroundings of thethick-walled portion 11 in a distributed state, it is possible to renderthe contact area of the elastic partition membrane 10 with the platemembers 84, 94 (the displacement-regulating portions 84 c, 94 c) smalland accordingly, to suppress effectively the generation of strangesounds ascribed to impingement of the elastic partition membrane 10 onthe plate members 14,15 by that amount.

The respective ribs 14, 15 are arranged in a radial fashion relative tothe axis center of the thick-walled portion 11 and at equal intervals ofabout 45 degrees in the circumferential direction. Further therespective ribs 14,15 are disposed in a mutually superposed positionwhen viewed in the axial center direction. Therefore when a relativelylarge amplitude vibration is input and the first and the second ribs 14,15 abut (impinge) on the plate members 84, 94 (thedisplacement-regulating portions 84 c, 94 c), it is possible to supportthe thick-walled portion 11 from its surroundings with a uniform force,so that it is possible to prevent the force from acting unevenly on thethick-walled portion 11, thereby elevating the durability andconcurrently enhancing more efficiently the membrane stiffness.

As shown in FIG. 6, the first and the second ribs 14, 15 are set to beapproximately the same in height dimension from the thin-walled portion12 as that of the thick-walled portion 11, and formed respectively withthe top portion 14 a and the top portion 15 a at the upper end face andthe lower end face (the upside face and the downside face in FIG. 6) ina projecting manner. In the assembling state of the partitioning means7, only the top portions 14 a, 15 a abut on the plate members 84, 94(the displacement-regulating portions 84 c, 94 c).

Therefore where the first and the second ribs 14, 15 impinge on theplate members 84, 94 (the displacement-regulating portions 84 c, 94 c)attended with inputting of a relatively large amplitude vibration, thetop portions 14 a, 15 a resist such that it is possible to make thefirst and the second ribs 14,15 to impinge mildly on the plate members84, 94, so that it is possible to securely reduce the generation ofstrange sounds.

Further because it is only the top portions 14 a, 15 a low in stiffnessthat abut on the plate members 84, 94 in the steady state, it ispossible to suppress the obstruction of reciprocating displacement ofthe elastic partition membrane 10 to the minimum, thus deforming theelastic partition membrane 10 sufficiently, complying with the hydraulicpressure fluctuations between the first and the second liquid chambers6A, 6B by. As a result, where a relatively small amplitude vibration isinput, the hydraulic pressure difference between the first and thesecond liquid chambers 6A, 6B can be efficiently absorbed, therebyobtaining reliably a low dynamic spring characteristic.

The top portions 14 a, 15 a may be configured in the form of acircumferentially contiguous raised body or a conical protruding body atthe upper end face and the lower end face of the first and the secondribs 14,15.

The elastic partition membrane 10 is constructed, on the one face sideand the other face side, in the same pattern (position, size, shape,etc.) and in a symmetry relative to a plane passing through the midwayin the thickness direction and a rotation symmetry relative to the axiscenter. That is, the elastic partition membrane has not thedirectionality of its upside and downside and the directionality of itsrotational direction, and consequently, in the assembling process of thepartitioning means 7 it is unnecessary to take account of the assemblingdirection of the elastic partition membrane 10, so that the assemblingwork can be simplified to curtail the working cost.

The invention has been described so far on the basis of the workingembodiment, but it will be appreciated that this invention is notlimited to the embodiment described above, but various variations ormodifications can be made within the scope of this invention withoutdeparting from the purport of the invention.

For instance, although no particular mention has been made in the aboveembodiment, it is alternatively possible to provide auxiliary ribs atleast on one face side of the thin-walled portion 12. The heightdimension of the top portions 14 a, 15 a of the first and the secondribs 14, 15 may be set so that they may be spaced apart from the platemembers 84, 94 (the displacement-regulating portions 84 c, 94 c).

As a variation example, this particular constitution will be nowdescribed with reference to FIG. 8. FIG. 8(a) is a top plan view ofanother elastic partition membrane 210 in a variation example, and FIG.8(b) is a partially enlarged sectional view of the elastic partitionmembrane 210 taken along VIIIb-VIIIb line in FIG. 8(a). The partssimilar to those in the aforesaid embodiment are designated by likereference numerals, and detailed explanation of them is omitted.

At the thin-walled portion 212 of the elastic partition membrane 210, asshown in FIG. 8, a plurality of the auxiliary ribs 216 are formed in aradial and rectilinear fashion and in an annular fashion centering onthe axis center. The auxiliary ribs 216 are formed, on the one face sideand the other face side of the thin-walled portion 212, in the samepattern (position, size, shape).

As a consequence, it is possible to fortify the thin-walled portion 212,which is inferior in strength among the elastic partition membrane 210,so that it is possible to suppress a possible failure of the thin-walledportion 212 attended with the reciprocating displacement upon inputtingof vibration, thereby enhancing the durability.

As shown in FIG. 8, the auxiliary ribs 216 are constructed to be lowerin rib height and narrower in rib width than the first and the secondribs 214, 215, so that it is possible to restrain a rise in stiffness ofthe elastic partition membrane 210 as a whole thereby maintaining a lowdynamic spring characteristic when a relatively small amplitudevibration is input.

On the other hand, where the thin-walled portion 212 impinges on theplate members 84, 94 (the displacement-regulating portions 84 d, 84 e,94 d, 94 e), accompanied by inputting of a relatively large amplitudevibration, the auxiliary ribs 216 serve as a cushion, allowing thethin-walled portion 212 to impinge mildly on the plate members 84, 94,and consequently, it is possible to reduce more securely the generationof strange sounds.

Further the thick-walled portion 211 and the first and the second ribs214, 215 are, as shown in FIG. 8(b), set to be lower in height dimensionthan those in the aforesaid embodiment. In the assembled state of thepartitioning means 7, the top portions 214 a, 215 a of the first and thesecond ribs 214, 215 are set in such a height dimension that they aresituated to be spaced apart from the plate members 84, 94 (thedisplacement-regulating portions 84 c, 94 c).

As a result, it is possible to render it easier for the elasticpartition membrane 210 to do a reciprocating displacement, therebyfacilitating more its submissive deformation in response to thehydraulic pressure fluctuatons between the first and the second liquidchambers 6A, 6B, so that when a relatively small amplitude vibration isinput, it is possible to absorb efficiently the hydraulic pressuredifference between the first and the second liquid chambers 6A, 6B toobtain more securely a low dynamic spring characteristic.

In the case where the first and the second ribs 214, 215 impinge on theplate members 84, 94 despite the fact that in order to obtain a lowdynamic spring characteristic, the top portions 214 a, 215 a are set ina height dimension so as to be spaced apart from the plate members 84,94 in this manner, the top portions 214 a, 215 a serve as a cushionthereby enabling the first and the second ribs 214, 215 to impingemoderately on the plate members 84, 94, so that it is possible toachieve a great reduction of strange sounds by that amount.

In the foregoing embodiment, the inner periphery of the engine sidebracket B2 is configured in a rectilinear shape in cross-section, but isnot necessarily limited to this shape. Alternatively the inner peripheryof the engine side bracket B2 may be formed with an abutment portioncapable of abutting on the step portion of the second attachment fitting2 internally press-fitted therein in such a manner that the abutmentportion protrudes radially inwardly.

Another variation example of this constitution will be described withreference to FIG. 9. FIG. 9 is a sectional view of the hydraulicantivibration device 100 in the variation example and corresponds to thesectional view of the hydraulic antivibration device 100 taken alongII-II line of FIG. 1(a). Like parts in the foregoing embodiment aredesignated by like reference numerals, and detailed explanation of themis omitted.

As illustrated in FIG. 9, at the inner periphery of the engine sidebracket B12 an abutment portion B12 b is formed to protrude radiallyinwardly. Thus when the second attachment fitting 2 is internallypress-fitted in the inner periphery of the engine side bracket B12, thestep portion is put into abutment on the abutment portion B12 b, wherebyit is possible to conduct the positioning of press-fitting direction.

The second attachment fitting 2 is constructed so that thelarge-diameter cylinder portion 2 a may be situated on the firstattachment fitting 1 side than the small-diameter cylinder portion 2 b,and in the internal press-fitting state as shown in FIG. 9, the stepportion of the second attachment fitting 2 may be situated on the firstattachment fitting 1 side than the abutment portion B12 b of the engineside bracket B12.

Because of that construction, in cases where the engine EG aftersupported and fixed displaces largely owing to irregularity of thetravelling road surfaces and the engine side bracket B12 is displacedlargely in the carrying load direction (the downward direction in FIG.9) (namely, where the second attachment fitting 2 is displaced towardthe first attachment fitting 1), the elastic recovery force of thecompression-deformed vibration-isolating base 3 works as a forceobstructing the movement of the second attachment fitting 2, and thesecond attachment fitting 2 becomes liable to be detached from the innerperiphery of the engine side bracket B12. However, according to thehydraulic antivibration device 100 in this variation example, becausethe abutment portion B12 b of the engine side bracket B12 is made toabut on the step portion of the second attachment fitting 2, suchdetachment of the second attachment fitting 2 from the inner peripheryof the engine side bracket B12 can be avoided reliably.

Where the engine side bracket B12 is displaced in the opposite direction(upward direction in FIG. 9) to the carrying load (namely, the secondattachment fitting 2 is displaced in a receding direction from the firstattachment fitting 1), the elastic recover power of thecompression-deformed vibration-isolating base 3 acts as power aiding inthe movement of the second attachment fitting 2 and consequently, thesecond attachment fitting 2 is hard to be detached from the innerperiphery of the engine side bracket B12. Therefore such a preventivemeans to detachment as described above is dispensed with.

In the foregoing embodiment, the description has been made of the casewhere the large-diameter cylinder portion 2 a of the second attachmentfitting 2 is internally press-fitted in the inner periphery of theengine side bracket B2, but the invention is not necessarily limited tothis embodiment. Instead, it is possible to construct so that thesmall-diameter cylinder portion 2 b of the second attachment fitting 2may be internally press-fitted in the inner periphery of the engine sidebracket B2.

In that case constructed in this manner, the step portion of the secondattachment fitting 2 can be brought into abutment on the opening of theengine side bracket B2, and consequently, it is possible to conduct thepositioning upon internal press-fitting and to obtain a detachmentprevention effect, similarly to the case where the above-mentionedabutment portion B12 b is provided.

In the foregoing embodiment, the description has been made of the casewhere the first and the second ribs 14, 15 of the elastic partitionmembrane 10 are arranged in a mutually superposed position when viewedin the axis center direction, but otherwise, the first ribs 14 may bearranged to be deviated in the circumferential direction from the secondribs 15 when viewed in the axis center direction.

This deviated arrangement is possible, for example, in the followingway: In the foregoing example, the first and the second ribs 14, 15 aredisposed at intervals of 45 degrees in the circumferential direction.Here, the position of the respective second ribs to be arranged is movedby 22.5 degrees relative to the position of the respective first ribs 14to be arranged so that when viewed in the axis center direction, each ofthe second ribs 15 may be situated in the intermediate between the firstribs 14 mutually adjacent.

Thus for example, where the first ribs 14 are displaced toward the platemember 84, attended by the input of a relatively large amplitudevibration, in particular, after the first ribs 14 abut on the platemember 84, the second ribs 15 situated oppositely to the displacementdirection of the first ribs act as a reinforcing member to regulate thedisplacement of the elastic partition membrane 10 (the thick-walledportion 11 and the thin-walled portion 12), which makes it difficult forthe elastic partition membrane 10 to displace, thus enabling enhancementof the membrane stiffness by that amount. As a result, it is possible toexhibit more the fluidization effect of the fluid to obtain a highdamping characteristic.

On the other hand, against the input of a relatively small amplitudevibration, the number of the first and second ribs 14, 15 disposed isnot changed from the number in the foregoing embodiment, andconsequently, a rise in stiffness of the entirety of the elasticpartition membrane 10 is suppressed and a low dynamic springcharacteristic can be maintained.

Although explanation was omitted in the foregoing embodiment, such aconstitution is also possible that rubber-like elastomer is attachedrespectively to the inner peripheral face of the body frame side bracketB1 (inner peripheral face of a space accommodating the hydraulicantivibration device 100) and to the outer peripheral face of the engineside bracket B2 by vulcanization bonding, etc., thereby enablingregulation of the displacement so that a stopper action may be obtainedupon inputting of a large displacement.

1. A hydraulic antivibration device comprising a first attachmentfitting, a second cylindrical attachment fitting, a vibration-isolatingbase joining the second attachment fitting and the first attachmentfitting and composed of a rubber-like elastomer, a diaphragm attached tothe second attachment fitting and forming a liquid-filled chamberbetween the diaphragm and the vibration-isolating base, partitioningmeans comparting the liquid-filled chamber into a first liquid chamberon the vibration-isolating base side and a second liquid chamber on thediaphragm side, and an orifice formed between an outer peripheral faceof the partitioning means and an inner peripheral face of the secondattachment fitting and putting the first liquid chamber and the secondliquid chamber into communication with each other, the partitioningmeans including an elastic partition membrane composed of a rubber-likeelastomer and a pair of displacement-regulating members regulating thedisplacement amount of the elastic partition membrane from both sidesthereof, the pair of displacement-regulating members having respectivelyopenings; which device is characterized in that the openings consist ofa first opening defined on a radially central side of each of thedisplacement-regulating members and a plurality of second openingsdefined around the first opening in a distributed manner; the elasticpartition membrane includes a thick-walled portion on a radially centralside thereof located within the first openings when viewed in an axiscenter direction thereof, a thin-walled portion located radiallyoutwardly of the thick-walled portion and formed to be thinner than thethick-walled portion thereby being located to be spaced apart from thepair of the displacement-regulating members, a stationary portionsituated in a peripheral marginal area of the thin-walled portion andpinched and fixed between the pair of the displacement-regulatingmembers radially outwards of the second openings, first ribs situated,on the one face side of the thin-walled portion, around the thick-walledportion in a distributed manner and formed integrally with a boundarybetween the thick-walled portion and the thin-walled portion in a spacedrelation to the one of the pair of the displacement-regulating members,and second ribs situated on the other face side of the thin-walledportion around the thick-walled portion in a distributed manner andformed integrally with the boundary between the thick-walled portion andthe thin-walled portion in a spaced relation to the other of the pair ofthe displacement-regulating members; the first attachment fitting isconstructed as a body frame side coupling means to be coupled to thebody frame side and the second attachment fitting is constructed as avibration generator side coupling means to be coupled to the vibrationgenerator side, and thereby, part of a vibration transmitting path fromthe partitioning means to the body frame is constituted by thevibration-isolating base.
 2. The hydraulic antivibration device as setforth in claim 1, which is characterized in that the first and thesecond ribs are disposed, when viewed in the axis center direction ofthe elastic partition membrane, in a radial fashion relative to the axiscenter and equidistantly in the circumferential direction.
 3. Thehydraulic antivibration device as set forth in claim 1 or 2, which ischaracterized in that the first and the second ribs have respective topportions on their opposing faces to the pair of thedisplacement-regulating members in a projecting manner and the topportions are set in such a height dimension that upon assembling of thepartitioning means, the top portions may be situated in a spacedrelation to the pair of the displacement-regulating members.
 4. Thehydraulic antivibration device as set forth in claim 1 or 2, which ischaracterized in that the first and the second ribs have respective topportions on their opposing faces to the pair of thedisplacement-regulating members in a projecting manner and the topportions are set in such a height dimension that upon assembling of thepartitioning means, the top portions may abut on the pair of thedisplacement-regulating members.
 5. The hydraulic antivibration deviceas set forth in claim 1 or 2, which is characterized in that on at leastone face side of the thin-walled portion, auxiliary ribs are formed in aresidual space of a space where the first or the second ribs are formed,and the auxiliary ribs are constructed to be lower in rib height andnarrower in rib width than at least the first or the second ribs.
 6. Ahydraulic antivibration assembly containing the hydraulic antivibrationdevice as set forth in claim 1 or 2 and a vibration generator sidebracket coupling the hydraulic antivibration device to the vibrationgenerator side bracket, which assembly is characterized in that thesecond attachment fitting includes a small-diameter cylinder portion, alarge-diameter cylinder portion formed to be larger in diameter than thesmall-diameter cylinder portion, and a step portion linking thelarge-diameter cylinder portion and the small-diameter cylinder portion,the large-diameter cylinder portion being internally press-fitted in theinner periphery of the vibration generator side bracket; the vibrationgenerator side bracket is formed on its inner periphery with an abutmentportion protruding radially inwardly that is capable of abutting on thestep portion of the second attachment fitting internally press-fitted inthe inner periphery.
 7. The hydraulic antivibration assembly as setforth in claim 6, which is characterized in that the second attachmentfitting is constructed so that the large-diameter cylinder portion maybe situated on the first attachment fitting side than the small-diameterattachment fitting, and internally press-fitted in the inner peripheryof the vibration generator side bracket, and that the step portion ofthe second attachment fitting in the internally press-fitted state maybe situated on the first attachment fitting side than the abutmentportion of the vibration generator side bracket.